Most fiber optic components, such as fused-fiber devices, are fragile components and need to be protected from environmental influences and other abuses both during use and during production. In particular, fused-fiber devices are formed by fusing and tapering two or more optical fibers together. Generally, fiber optic components, and in particular fused-fiber devices, are sensitive to environmental influences because the optical material of which the optical fibers are made is very fragile. In the case of fused-fiber devices, the fused region is particularly sensitive to adverse environments which can influence the quality of the optical material of the fused-fiber device and/or the signals transmitted through the fused-fiber device.
In operation of the fused-fiber device a portion of the optical power launched into the device is unavoidably converted into heat because of internal leakage of light power into its packaging through optical loss. For high optical power applications, the resulting temperature rise caused by power loss can cause internal heating of the packaged device sufficient to degrade the packaging and/or compromise the performance of the device. Heat generated within the device conducts to the exterior of the package and dissipates to the environment generally by an external heat sink to which the package exterior is in thermal contact and, in some arrangements, aided by forced air convection or coolant fluid, such as in an active cooling loop.
There is an increasing demand for fused-fiber devices whose packaging is more efficient at conducting internally generated heat to the external heat sink and thus are reliably able to transmit higher optical powers. Both power handling and reliability are generally significantly affected by the packaging of the device. Packaged fused-fiber devices are commonly produced with housings of circular or rectangular profile. Inside the housing is generally a substrate upon which a suitable affixment material is applied on or proximate to the fused portion on both sides of the fused portion. It is generally within this affixment material that optical loss from the fiber first appears as heat. The substrate conventionally has a D-shaped or slab-shaped geometry, and may have a slotted region in which to locate the fused portion of the device. The substrate material is generally selected for mechanical strength and for an expansion coefficient matched to that of the optical fiber material (e.g. silica). As a result the substrate material may not provide optimum thermal conductivity.
Slotted substrates provide convenient protection of the fused portion of the device during production. However, slotted thin substrates have increased thermal stressing of the slot resulting from thermal coefficient mismatch between the affixment and the substrate materials. Due to the resulting potential for fracture of the substrate proximate to the slot under conditions of temperature cycling or significant internal generation of heat, slotted thin substrates may be unsuitable for applications involving high optical power where long term reliability is needed.
D-shaped substrates for circular housings and the related slab-shaped substrate for rectangular housings provide alternative packaging configurations for generally improved reliability as compared to slotted substrates.